Vacuum plasma processors are used to deposit materials on and etch materials from workpieces that are typically semiconductor, dielectric and metal substrates. A gas is introduced into a vacuum plasma processing chamber where the workpiece is located. The chamber pressure is typically in the range of 0.1 to 1000 torr. The gas is ignited into an RF plasma in response to an RF electric or electromagnetic field. The RF field is provided by a reactive impedance element, usually either an electrode array or a coil which couples both magnetic and electrostatic RF fields to the gas. The reactive impedance element is connected to a first RF source having a first relatively high RF frequency and sufficient power such that the gas is ignited into the plasma. Connections between the first RF source and reactive impedance element are usually by way of a relatively long cable, connected directly to the first RF source. A first resonant matching network connected between the cable and reactive impedance element usually includes a pair of variable reactances adjusted to match the impedance of the first RF source to the load it is driving.
Typically, the gas is introduced into the chamber through the top of the chamber and is withdrawn from the bottom of the chamber. It is common for an electrode at the top of the chamber to be associated with a series of baffles and openings into the excitation region to provide a shower head effect for the gas flowing into the excitation region.
The workpiece is usually mounted on an electrode at the bottom of a plasma excitation region in the chamber. In some chambers, the electrode carrying the workpiece is the reactive impedance element supplied with the first RF frequency and another electrode spaced from the electrode carrying the workpiece is connected to a reference potential, typically ground. As illustrated in FIG. 4 of the previously mentioned co-pending provisional application, it is known to provide such a chamber with exterior walls and a plasma confinement region within the interior of the chamber.
In other chambers, the reactive impedance element is spaced from the electrode carrying the workpiece at the bottom of the excitation region. In some of these other chambers, as illustrated in FIG. 1 of the co-pending previously mentioned provisional application, the reactive impedance element is a coil adjacent to the top of the excitation region and the electrode carrying the workpiece is frequently connected to a second RF source having a second RF frequency considerably lower than the first RF frequency. The second RF source, frequently referred to as a DC bias source because it causes a DC voltage to be established on the electrode, is usually connected to the electrode by a second resonant matching network, also usually including a pair of variable reactances adjusted to match the impedance of the second RF source to the load it is driving. If the reactive impedance element is a coil, the second RF source typically has a frequency in the 2 MHz range. In these other chambers, the coil is located outside the chamber and the electromagnetic field produced in the coil is coupled to gas in an excitation region of the chamber through a dielectric window at the top of the chamber.
The first, relatively high frequency, which is in excess of 10 MHz, controls the density of the plasma, while the second, relatively low frequency, which is less than 10 MHz, controls the energy of ions in the plasma. Independent control of plasma density and ion energy is provided by independently controlling electric parameters, such as power, voltage and/or current, of the first and second RF sources. These other vacuum chambers include a metal wall, usually maintained at a reference potential, for example ground.
In still other chambers, wherein the electrode at the top of the excitation region is connected to a reference potential, the first, relatively high RF frequency is supplied to the metal wall, which functions as the reactive impedance element, while the second, relatively low RF frequency is supplied to the electrode carrying the workpiece. When the vacuum chamber includes a metal wall, the metal wall usually defines the exterior of the plasma excitation region.
In still further configurations, the chamber wall is an insulator and the exterior of the plasma excitation region is defined by plasma confining louvers spaced from the chamber wall and maintained at a reference potential, such as ground. The gas which is excited to a plasma in the excitation region flows through the louvers to an outlet port at the bottom of the chamber. In these further configurations, the electrode at the top of the excitation region is connected to the reference potential.
While the foregoing structures have been adequate for processing prior art workpieces, they are not believed to be adequate to handle deep submicron processing of workpieces, particularly semiconductor wafers meeting increased requirements for etching and deposition of films. Key design parameters for plasma processors meeting these increased requirements are generating and maintaining the correct ratio of ions and radicals to neutral species in the plasma, the residence time of the ions, radicals and neutral species in the excitation region above the workpiece and control of the energy of ions incident on the substrate. These parameters provide wide process control to develop the correct processes for many types of etch and deposition processes. In addition, for workpieces having large areas, the cost of processing each workpiece has become an important parameter in processor design. The mean time between cleaning the chamber interior, the cost of consumables, serviceability of the processor and numerous other factors affect the cost of processing a workpiece in the processor.